1. Field of the Invention
The invention pertains to methods for manufacturing articles, called optical assemblies, which comprise optoelectronic devices (such as LEDs or PIN diodes) and are adapted for attachment to lightwave channels, such as optical fibers, for efficiently coupling light into or out of the optoelectronic devices.
2. Art Background
In optical communication systems, a variety of devices, conventionally called optoelectronic devices, are used to convert electrical signals into corresponding optical signals, and vice versa. Included among these optoelectronic devices are semiconductor diode lasers and light emitting diodes (LEDs), used to convert electrical signals into optical signals, and PIN diodes, used to detect optical signals and convert them into electrical signals.
In use, an optoelectronic device is typically incorporated into an apparatus called an optical subassembly (OSA) which, in turn, is incorporated into an apparatus called an optical assembly (OA). That is, an OSA conventionally includes an optoelectronic device mounted upon a support member. The OA includes the OSA and often also includes a circuit board on which the support member is mounted, as well as, in many instances, additional electronic devices mounted, for example, on the support member or on the circuit board. The OA often further includes a housing within which the OA and circuit board are fully or partially enclosed.
The OA is adapted to be connected to a lightwave channel, such as an optical fiber or an optical connector, for efficiently coupling light into or out of the optoelectronic device. To achieve such coupling, the OA typically (although not necessarily) includes a receptacle for receiving the connector or the end of the optical fiber nearest the optoelectronic device. When used, the receptacle is, for example, either mounted on or formed in the support member of the OSA, or, more typically, is mounted on a separate support member.
Significantly, although the optoelectronic devices and the component piece parts of OSAs and OAs are typically mass produced, the OSAs and OAs themselves are conventionally individually manually fabricated and/or assembled, one at a time. That is, each OSA is currently individually fabricated by forming a pattern of strip-like metallic conductors extending between metallic contacts, using conventional silk-screen processing, on the surface of an individual, typically a molded ceramic, support member. An optoelectronic device is manually mounted on the support member by soldering the electrical contacts of the optoelectronic device to certain of the metallic contacts on the support member (electrical communication thus being achievable with the optoelectronic device via other metallic contacts on the support member which are electrically connected to the mounting contacts through the strip-like conductors). Then, the OSA, i.e., the support member bearing the optoelectronic device, and the support member bearing the receptacle for the optical fiber or connector are manually installed in the OA.
After installation, but before the corresponding support members are permanently fixed in relation to one another, the optoelectronic device and lightwave channel are actively aligned, to optimize the coupling of light between the former and the latter. During active alignment, the optoelectronic device is operated, and either the support member bearing the optoelectronic device or the support member bearing the lightwave channel is moved while the output of the optoelectronic device (i.e., the electrical output or the light emanating from, for example, the distal end of the optical fiber) is monitored until an acceptable output is achieved. Once acceptable alignment is attained, the support members are fixed in position, typically by soldering or adhesive attachment. Alternatively, if the lightwave channel is, for example, an optical fiber end is initially held loosely enough within its receptable to permit moving the fiber to achieve the desired alignment. If so, then after alignment the fiber is secured, for example, with epoxy adhesive.
A significant drawback associated with the current method of individually fabricating OSAs and OAs is the need for manual piece-part handling, which is expensive and limits throughput. In this regard, it has been suggested (although no concrete proposals have ever been formulated) that the cost of manufacturing OAs might be reduced, and throughput increased, if mass production methods could be used to reduce or eliminate the relatively expensive manual handling steps.
Yet another drawback of the current OA fabrication method is the need for active alignment, which also reduces throughput and also increases manufacturing costs. In this regard, as noted, the support member of an OA is conventionally a ceramic part typically processed using conventional fabrication techniques. Significantly, conventional fabrication tolerances are no better than about 100 micrometers. However, single-mode optical fibers must be aligned with optoelectronic devices such as semiconductor lasers or LEDs to within tolerances of less than one micrometer, and multi-mode fibers must be aligned to within tolerances of less than eight micrometers. Because conventional machining is incapable of achieving such tolerances, conventional OAs must necessarily be actively aligned to the optical fibers or connectors to which they are mated. In this regard, it is believed that significant reductions in manufacturing cost could be achieved, at least for multi-mode fiber coupling, if, for example, alignment features for positioning the fiber could be made accurately enough to eliminate the need for active alignment. Even if active alignment were still required, very precise alignment features would still simplify the active alignment step by providing an initial coarse alignment.
Still another drawback of the conventional OA fabrication method is the use of silk-screen processing, which is incapable of forming conductors with precisely controlled dimensions. Consequently, some OAs manufactured by conventional methods suffer undesirably high capacitance due to excessive conductor dimensions, which limits the speed of operation and/or reduces the sensitivity of the corresponding optoelectronic devices.
In some instances, the conventional OA fabrication method involves other production processes that add cost and reduce throughput. For example, for certain optoelectronic devices, e.g., some LEDs, it is common practice, prior to incorporation into OSAs and OAs, to operate the devices for a predetermined period of time at an elevated temperature, to induce failure in those that are defective. This procedure is referred to as "burn-in." Groups of optoelectronic devices are conventionally burned in by repetitiously placing individual devices, one-by-one, on a test rack, and operating the devices. Introduction of an appropriate mass-handling technique could reduce the cost of mass burn-in and mass testing by eliminating repetitious steps.
U.S. Pat. No. 4,779,946 and U.S. Pat. No. 4,826,272 describe a method for fabricating OAs in which silicon, rather than ceramic, support members are employed. In accordance with the teachings of these patents, a plurality of these silicon support members are simultaneously fabricated by initially lithographically patterning a silicon substrate. The patterned silicon substrate is then subdivided into individual members, and individual optoelectronic devices are mounted on the individual support members to form OSAs, which are incorporated into OAs. While this patented method does achieve increased throughput, still higher throughputs are needed, as discussed below.
Until recently, the main application envisioned for OAs has been in long-distance communication. This application has generated a relatively small demand for OAs, typically several thousand per year. Although the manufacture of an OA requires relatively intensive use of manual labor, the manufacturing cost has been tolerated because the demand for OAs has, until now, been relatively small.
Significantly, optical communication links are currently being considered for short-haul communication. This application is expected to generate a much greater demand for OAs, typically several million per year. In order to fill a demand of this magnitude and still keep the application economically feasible, it is advantageous to decrease the manufacturing cost of OAs and increase the throughput by a significant factor. Consequently, practitioners in the art of OA manufacturing have sought a manufacturing method that achieves both a substantial reduction in cost and a substantial increase in throughput.